1. Field of the Invention
This invention relates to improvements in a fuel injection system for use in an internal combustion engine.
2. Description of the Prior Art
FIG. 1 is a block diagram showing a conventional fuel injection system for use in an internal combustion engine. The system comprises an air flow sensor 1 responsive to an intake air flow for developing at its output a voltage signal Sq having a magnitude proportional to the intake air flow and a rotation sensor 2 responsive to a speed of rotation of the engine for developing at its output a voltage signal Sn having a magnitude proportional to the engine rotational speed. The signals Sq and Sn are fed to a divider 3 which develops at its output a signal Sq/Sn having a magnitude corresponding to the intake air flow per an engine rotation. The signal Sq/Sn is fed to a basic pulse generator 4 which develops at its output a basic pulse signal Sp1, the pulse width of which corresponds to the magnitude of the signal Sq/Sn. The basic pulse signal Sp1 is fed to a correction circuit 5 which corrects the pulse width of the basic pulse signal Sp1 in accordance with signals S1 to S5 fed thereto from sensors (not shown) and representing various engine operation parameters such as throttle position, water temperature, outside temperature, engine rotational speed and exhaust gas condition and develops at its output a pulse signal Sp2 having a corrected pulse width. The pulse signal Sp2 is applied to a drive circuit 6. The drive circuit 6 provides an injection pulse P1 having its pulse width determined by the pulse signal Sp2 to an electromagnetic fuel injection valve 7 every time a timing signal St1 is applied thereto in synchronism with rotation of the engine so that the fuel injection valve 7 is actuated to inject fuel for a period of time corresponding to the pulse width of the injection pulse P1.
The general principle of such a conventional fuel injection system is to effect fuel injection for each engine rotation under the control of an injection pulse, the pulse width of which is determined in accordance with the intake air flow per one engine rotation. That is, the amount of fuel to be injected is controlled in accordance with the pulse width of the injection pulse. This requires a highly precise and expensive injection valve which is operable with high responsibility to the injection pulses and also which has a large flow dynamic range such as one on the order of 10:1. Additionally, the conventional fuel injection system requires a complex control circuit which includes a divider for calculating an intake air amount per one engine rotation.